Ultrafast response induced by interference effects between weakly confined exciton states
Ultrafast response induced by interference effects between weakly confined exciton states
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DOI：
10.1143/jpsj.77.044701
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发表时间：
2008-04-01
影响因子：
1.7
通讯作者：
Tsuchiya, Masahiro
中科院分区：
文献类型：
--
作者：
Kojima, Osamu;Isu, Toshiro;Tsuchiya, Masahiro
我们报告了通过简并四波混频（DFWM）技术观察到的 GaAs 薄膜中弱约束激子的超快响应。宽带脉冲激发的时域信号呈现出周期随脉冲谱宽变化的振荡结构，并具有与脉冲宽度相当的超快响应；另一方面，激子失相时间几乎不受激发谱宽度的影响。这种超快响应比根据非局域响应理论预期的辐射寿命快得多。在不同时间延迟下测量的 DFWM 光谱清楚地表明弱约束激子对超快响应的贡献。此外，在激发能量依赖性的测量中，受控谱宽激发的时域信号表现出振荡周期和响应时间的变化。这些特性与激发光谱宽度依赖性的特性相似。通过对振荡结构的分析，发现振荡源于弱约束激子态之间的干扰。因此，我们得出结论，由于 DFWM 信号的干扰而导致的振荡重叠导致了超快响应，而激子相移时间没有任何变化。这些结果意味着激发光谱宽度的控制会引起弱约束激子的超快非线性光学响应。
We report an ultrafast response of weakly confined excitons in GaAs thin films observed by a degenerate four-wave-mixing (DFWM) technique. The time-domain signals excited by broadband pulses show an oscillatory structure with a period that varies according to the pulse spectral width and an ultrafast response comparable to the pulse width; on the other hand, the exciton dephasing time is hardly changed by the excitation spectral width. This ultrafast response is much faster than the radiative lifetime expected on the basis of the nonlocal response theory. The DFWM spectra measured at various time delays clearly indicate the contribution of weakly confined excitons to the ultrafast response. Moreover, in the measurement of excitation-energy dependence, the time-domain signals excited by a controlled spectral width exhibit the variation of the oscillation period and response time. These characteristics are similar to those of the excitation spectral width dependence. From the analysis of oscillatory structures, it is found that the oscillation originates from the interference between weakly confined exciton states. Therefore, we conclude that the overlap of the oscillation due to the interference with the DFWM signal leads to the ultrafast response without any change in the exciton dephasing time. These results imply that the control of the excitation spectral width induces the ultrafast nonlinear optical response of the weakly confined excitons.